It's the beginning of spring in the Southern Hemisphere - the time of year
when the so-called "ozone hole" forms over Antarctica.

Now, this isn't a "hole" in the atmosphere, it's just a reduction in the
amount of one gas - ozone - 10 to 30 miles up. This decrease is linked to
human-made chemicals called chlorofluorocarbons - CFCs for short. The chlorine
in CFCs destroys ozone, and the bitter cold high above Antarctica helps the process
along.

This year, the ozone hole was the largest ever observed - three times the area
of the United States. In these
striking images from NASA,
the ozone hole is the
bluish-purple oval-shaped area
centered over Antarctica. The huge size of
the hole this year is disappointing, because concentrations of CFCs have
actually leveled off in recent years, and the long-term prognosis is for the
ozone hole to get smaller. This year's record-setter clearly shows that we
still have a long way to go before this environmental problem is fixed.